For various reasons associated in particular with better comfort of use (softness, emollience and the like), current cosmetic or dermatological compositions are usually in the form of an emulsion of the oil-in-water (O/W) type, i.e. a support consisting of an aqueous dispersing continuous phase and an oily dispersed discontinuous phase. These O/W emulsions are more in demand than emulsions of the water-in-oil (O/W) type, which consist of a fatty dispersing continuous phase and of an aqueous dispersed discontinuous phase, since they give the skin on application a softer, less greasy and lighter feel than the W/O emulsion systems.
Moreover, in cosmetics, dermatology and pharmacy, emulsions comprising small globules (or droplets) of the dispersed phase, also known as fine emulsions, are often desired, whether:                for their texture: the compositions may be more or less viscous and may range from the consistency of a lotion to that of a cream;        for their visual appearance, which may range from a transparent or opalescent composition to a white composition;        for their cosmetic feel that especially promotes their speed of penetration;        for their broad possible positioning in market terms, since such compositions satisfy consumers in both Europe and Japan and in other countries.        
In the present patent application, the term “fine emulsion” means an emulsion in which the size of the globules of the dispersed phase ranges from 50 to 500 nanometers.
In terms of technology, at the present time, to obtain fine O/W emulsions of this type, energy needs to be supplied to the mixture, either large mechanical energy in order to fragment the dispersed phase into fine globules, or thermal energy by proceeding via a process of change of phase with temperature (80° C.), for instance the systems prepared by the PIT “Phase Inversion Temperature” technique. These systems are well known and nowadays allow access to fine emulsions.
Thus, the technique of mechanical input of energy makes it possible to obtain fine transparent emulsions, also known as (nanoemulsions), described, for example, in documents EP-A-728 460, EP-A-780 114, EP-A-780 115, EP-A-879 589, EP-A-1 010 413, EP-A-1 010 414, EP-A-1 010 415, EP-A-1 010 416, EP-A-1 013 338, EP-A-1 016 453, EP-A-1 018 363, EP-A-1 020 219, EP-A-1 025 898, EP-A-1 120 102, EP-A-1 120 101, EP-A-1 160 005, EP-A-1 172 077 and EP-A-1 353 629. The oil globules of the nanoemulsions have a mean size of less than 100 nm. The drawback of these nanoemulsions is the need for large input of mechanical energy.
Nanoemulsions are also described in the publications by Forgiarini, J. Esquena, C. Gonzàlez and C. Solans, “Formation of Nano-emulsions by Low Energy Emulsification. Methods at Constant Temperature”, Langmuir, 2001, 17, 2076-2083H., and Forgiarini, J. Esquena, C. Gonzàlez and C. Solans, “Studies of the Relation Between Phase Behavior and Emulsification Methods with Nanoemulsion Formation”, Prog. Colloid Polym Sci., 2000, 115 (Trends in Colloid and Interface Science XIV), 36-39. These publications describe decane-in-water emulsions stabilized with a particular surfactant, laureth-4 (or Brij 30), and prepared by addition of water to a decane/Brij 30 mixture. The surfactant comprises a short (C12) alkyl chain, which makes it more irritant than its homologues with a longer alkyl chain. Moreover, the emulsions described in these documents are unstable, especially at the microscopic level (drop diameter) and are consequently too unstable for industrial application.
Moreover, the PIT technique is, in its principle, well known to those skilled in the art and is especially described in the articles “Phase Inversion Emulsification” by Th Farster et al, published in Cosmetics & Toiletries, vol. 106, December 1991, pp. 49-52, “Application of the phase-inversion-temperature method to the emulsification of cosmetics”, by T. Mitsui et al., published in American Cosmetics and Perfumery, vol. 87, December 1972, and in documents WO-A-89/11907, DE-A-4 318 171, EP-A-815 846 and EP-A-1 297 824.
However, these techniques for obtaining fine emulsions have the following drawbacks:                The high temperature of the PIT process imposes formulation constraints. Thus, it is difficult to use this technique with heat-sensitive molecules with low flashpoints, and the technique is thus limited to heat-insensitive molecules with high flashpoints. This restricts the type and number of starting materials that may be used, or alternatively, if it is desired to use, for example, molecules with low flashpoints, it is necessary, as a function of these starting materials, to adapt the procedure and these emulsions then become more complex and more expensive to obtain. As a result, this process excludes or at the very least limits the use of volatile compounds such as volatile lipophilic compounds, especially volatile oils, for instance volatile silicones, and certain heat-sensitive active agents or plant extracts.        High-pressure or very high-pressure homogenizers, which allow fine emulsions to be prepared by input of energy, are expensive and fragile items of equipment, which thus generate large industrial implementation costs.        
Moreover, transparent microemulsions are known in the prior art. Microemulsions are not strictly speaking emulsions, in contrast with nanoemulsions; they are transparent solutions of micelles swollen with oil, this oil generally being of very short chain length (e.g.: hexane or decane) and moreover being dissolved by means of the combined presence of a large amount of surfactants and cosurfactants forming the micelles. The swollen micelles are very small on account of the small amount of oil they are capable of dissolving. This very small size of the micelles is the reason for their transparency. However, unlike the nanoemulsions described above, microemulsions are formed spontaneously by mixing the constituents together, without any input of mechanical energy other than simple magnetic stirring, and irrespective of the order of addition of the constituents. In addition, they are thermodynamically stable systems. The major drawbacks of microemulsions are associated with their high proportion of surfactants relative to the oil, leading to intolerance and resulting in a tacky feel when applied to the skin. Moreover, the microemulsion state of the system is defined by the choice of constituents and their relative proportions, and also the temperature, as shown by the phase diagram presented in FIG. 11.7 of the article “The colloidal domain”, D. F. Evans, H. Wennerström, published by Wiley-VCH (1999). For the description of microemulsions, reference may be made, for example, to the article by M. Bourrel and R. S. Schechter “Microemulsions and related systems”, pages 25 to 30, published by Marcel Dekker, 1988. These microemulsions are therefore not fine emulsions and cannot overcome the drawbacks of the fine emulsions described above.
There is thus still a need to prepare fine O/W emulsions which remain stable when they are diluted and which are obtained via less expensive and less complex processes than those of the prior art, i.e. processes not requiring any energy input, whether this energy is mechanical or thermal, and thus without proceeding via high temperatures or without equipment that inputs a large amount of energy, these processes having no effect on the chemical stability of the compounds constituting the composition.